A hearing aid is a device which amplifies acoustic signal received with a microphone and outputs the amplified acoustic signal from a receiver.
A gain as a function of frequency is one of acoustic parameters to determine the acoustic characteristics of the hearing aid, and is defined as the ratio of amplitude of acoustic signal after amplified to amplitude of acoustic signal before amplified.
It is necessary to determine the acoustic characteristics so as to fit to the audibility of a user of the hearing aid.
A conventional hearing aid equips a plurality of filters, each of which is composed of a condenser and a resistor, and the acoustic characteristics of the conventional hearing aid is adjusted by adjusting the characteristic of the filter.
For example, when the hearing aid equips a high-pass filter composed of a condenser and a variable resistor, the attenuation amount of the low-frequency sound can be adjusted by changing a cut-off frequency which varies depending on the resistance value of the variable resister.
Similarly, when the hearing aid equips a low-pass filter, the attenuation amount of the high-frequency component can be adjusted.
As described above, the acoustic characteristic of the conventional hearing aid is determined by adjusting the attenuation amount of the filter.
Some conventional hearing aids equip an output limiter to limit the allowable maximum amplitude of the sound by adjusting the voltage of the power source.
The above-described conventional haring aid is adjusted by a person with a special skill who manually adjusts the variable resistors equipped on the hearing aid with a screw driver.
Recently, a programmable hearing aid providing an electrically erasable programmable memory (hereinafter referred to as EEPROM) and memorizing the set point of the variable register in the EEPROM, and a digital hearing aid, the acoustic characteristic thereof being precisely adjustable by digitally processing the acoustic signal have predominated.
To adjust the modern hearing aid, a hearing aid adjuster is applied.
The hearing aid adjuster determines a plurality of acoustic parameters to realize various acoustic characteristics in the hearing aid, and set the acoustic parameters into the EEPROM equipped on the hearing aid.
When the above-mentioned modern digital hearing aid predominates, the number of the adjustable characteristics, and the number of the acoustic parameters increase, and the number of the combination of the acoustic characteristics and the acoustic parameters becomes extremely big.
The foregoing hearing aid adjuster, however, entails a drawback that it requires long time, and monstrous burden not only of a user of the hearing aid, but also of a person adjusting the hearing aid, when examining all combinations and determining the optimum combination.
For resolving the above drawback, a hearing aid adjusting method applying the Simulated Annealing Method (hereinafter referred to as the SA Method) and/or the Genetic Algorithm Method (hereinafter referred as the GA Method) is already proposed (For example, refer to Patent Publications 1 and 2).
Many hearing aids adjusted with the hearing aid adjuster may require fine adjusting to satisfy the hearing aid user's requirements and to improve the acoustic characteristics.
Further, many hearing aid users may require readjusting of the hearing aid, after using the hearing aid adjusted by the hearing aid adjuster for a certain period.
Therefore, a person who finely adjusts the hearing aid, is required the professional skill to relate the acoustic parameters to the hearing aid user's requirements.
It is difficult, however, for a person with less-experience of adjusting the hearing aid to relate the acoustic parameters to the hearing aid user's requirements, and the person may fail to finely adjust the hearing aid.
Therefore, the hearing aid adjuster which shows changing amount of the acoustic parameters depending on the hearing aid use's requirement or moderately changes the acoustic parameters in accordance with operation of a button, has been applied (For example, refer to Patent Publication 3).
[Patent Publication 1] Unexamined patent publication No. H09-054765
[Patent Publication 2] Unexamined patent publication No. 2001-175637
[Patent Publication 3] Unexamined patent publication No. H02-20200